1. Field of the Invention
The present invention relates in general to an intraocular lens having a balloon member. The intraocular lens is filled by injection with a fluid after being inserted into a capsular bag normally containing the natural crystalline lens body (i.e., lens nucleus and lens cortex) of the human eye. More particularly, this invention is concerned with an intraocular lens which is free from leakage of the injected fluid from the balloon member, during and after the injection of the fluid into the lens.
2. Discussion of the Related Art
Intraocular lenses have been used, for example, as a dioptric substitute for rectifying one's eyesight after cataract surgery. Such lenses may be implanted in the anterior or posterior chamber of the eye, or may be supported by the iris. In particular, it is biologically natural and therefore desirable to replace the natural crystalline lens by the posterior chamber lens, that is, to insert such a lens in the capsular bag which has been emptied of the natural crystalline lens body.
Upon implantation of the intraocular lens in the capsular bag, the insertion of the lens in the eye requires the surgeon to make a scleral incision sufficiently large to allow the passage of the lens through the sclera. However, an excessively large incision will cause the patient to suffer from astigmatism after the surgery. Therefore, it is desirable that the intraocular lens is relatively small to allow insertion into the eye through a minimal incision.
To this end, there have been proposed some methods of inserting and fixing an intraocular lens in the capsular bag. For example, U.S. Pat. No. 4,449,257 discloses an intraocular lens made of water absorptive polymer containing hydroxyethyl methacrylate (HEMA). This lens is inserted into the eye while it is dry and small in size, and then expands and softens with uptake of aqueous humor to fill the capsular bag. In this case, the size of the scleral incision which allows the insertion of such a lens can only be reduced to about 4 mm, though it varies depending on the swelling rate of the lens material. Further, the intraocular lens placed in the capsular bag needs to freely expand and contract so as to closely follow the movement of the capsular bag. Preferably, the lens has the same shape as the crystalline lens body originally contained in the capsular bag, and is accommodated in the capsular bag in close contact with the inner surface thereof.
In view of the above situation, the inventors proposed an intraocular lens which consists of a balloon member formed of an elastomer, and an optically transparent fluid adapted to be injected into the balloon member, as disclosed in JP-A-63-200755, JP-A-64-32859 and JP-A-1-227753. The balloon member is inserted into the capsular bag which has been emptied of the crystalline lens body, and is then filled by injection with the transparent fluid so as to expand and fill the capsular bag. Thus, the balloon member filled with the fluid assumes substantially the same configuration as the natural crystalline lens body originally accommodated in the capsular bag.
Upon implantation of the intraocular lens as described above, the balloon member is folded into a compact form with the air or other gas removed from the member, to enable it to be inserted into the capsular bag. This makes it possible to reduce the size of the scleral incision for allowing the passage of the balloon member. Further, the balloon member assumes substantially the same shape as the crystalline lens body after the injection of the fluid, and is therefore properly fixed in position within the capsular bag. The thus obtained intraocular lens is able to closely follow the movement of the capsular bag, so as to adjust one's eyesight in the same manner as the natural lens.
In the intraocular lens as disclosed in JP-A-1-227753, the fluid is injected into the balloon member with use of a catheter, through a hollow tube provided on the balloon member. During the injection, however, the fluid in the balloon member may possibly leak from a clearance between the tube and the catheter. Otherwise, the injected fluid may leak through the tube, when the catheter is pulled out of the tube upon completion of the injection.
To avoid the leakage of the injected fluid, JP-A-63-200755 discloses a check valve formed at an inlet of the balloon member for the injection, while JP-A-64-32859 discloses a self-closure ring member mounted on the balloon member to automatically close or seal the balloon member. However, the check valve is rather complicated in construction, while the ring member need to be formed as a unit with the balloon member, resulting in cumbersome process for forming the lens. Thus, there is still plenty of room for improvement in the conventional intraocular lenses.